A standard six-high rolling stand of the type used for rolling strip steel has a pair of vertically spaced nip-defining working rolls of relatively small diameter. Respective upper and lower inner backup rolls of larger diameter bear respectively down and up toward the nip on the respective working rolls, and respective upper and lower outer backup rolls of still larger diameter bear toward the nip on the respective inner backup rolls. Thus the bendability of the small-diameter working rolls is largely canceled out by the rigidity of the larger-diameter backup rolls so that the large forces required for rolling can be brought to bear on the workpiece.
As described in "Herstellung von kaltgewalztem Band" (Volume 1 Verlag Stahleisen mbH, Dusseldorf, 1970, p309 and 310) working rolls of the smallest possible diameter are used for the most concentrated working effect. Lower limits are placed to the working roll size by such factors as the rolling and reaction forces that are transmitted as well as the angular forces that flow from the driven outer backup rolls. In addition the size of the stub shafts of the working rolls limits the amount of transverse stress that can be withstood, and the roll size itself determines when it will bend if stressed too much.
Accordingly it is known to brace the working rolls horizontally. German patent documents Nos. 3,335,857 and 3,335,858 describe systems that shift the working rolls axially, and so-called bottle rolls are used in German patent No. 3,038,865 require that the inner backup rolls be driven, a problem greatly complicated by the telescoping connection to the backup-roll ends. Thus it is standard to drive the outer backup rolls and have this rotation transmitted through the inner backup rolls to the working rolls. Passing such angular force through the inner backup rolls subjects them to bending stresses while greatly loading their bearings.